System and Method for TDD Configuration for D2D Open Discovery

ABSTRACT

Embodiments are provided to support device-to-device (D2D) communications in a time-division duplexing (TDD) communications system, and ensure that D2D discovery signals are transmitted by user devices on an uplink subframe when there is a TDD frame configuration change. In an embodiment, a user device receives form the network a TDD frame configuration selected from a set of available TDD frame configurations according to the TDD configuration. The device further receives a D2D discovery configuration for a discovery time interval. The user device then allocates a transmission resource a D2D discovery signal within the discovery time interval according to the D2D discovery configuration. The user device is also configured to receive from another device a second D2D discovery signal during the discovery time interval in accordance with the TDD configuration and the D2D discovery configuration.

This application claims the benefit of U.S. Provisional Application No.61/822,124 filed on May 10, 2013 by Philippe Sartori et al. and entitled“System and Method for TDD Configuration for D2D Open Discovery,” whichis hereby incorporated herein by reference as if reproduced in itsentirety.

TECHNICAL FIELD

The present invention relates to the field of network communications,and, in particular embodiments, to a system and method for time-divisionduplexing (TDD) configuration for device-to-device (D2D) open discovery.

BACKGROUND

Device-to-Device (D2D) technology is getting attraction because of theability to offer new services, improve system throughput, and offer abetter user experience. Potential use cases for D2D have been identifiedby the 3GPP Service and System Aspects working group 1 (3GPP SA WG1) inthe 3GPP Technical Report (TR) 22.803. However, in order for D2D to besuccessful and applicable to various deployment scenarios, there is needto ensure that D2D works for both time-division duplexing (TDD) andfrequency-division duplexing (FDD) systems.

SUMMARY OF THE INVENTION

In accordance with an embodiment, a method for device-to-device (D2D)discovery in time division duplexing (TDD) communications includesselecting, at a network component, a TDD frame configuration from a setof available TDD frame configurations, and sending, from the networkcomponent, an indicator of the TDD frame configuration to a plurality ofdevices. The method further includes determining a D2D discoveryconfiguration for a discovery time interval according to the TDD frameconfiguration, and sending, from the network component to the pluralityof devices, the D2D discovery configuration. The D2D discoveryconfiguration includes parameters enabling the devices to determinetransmission resources of D2D discovery signals and transmit the D2Ddiscovery signals during the discovery time interval.

In accordance with another embodiment, a method for D2D discovery intime TDD communications includes receiving, at a user device, anindicator of a TDD frame configuration selected from a set of availableTDD frame configurations, and further receiving a D2D discoveryconfiguration for a discovery time interval in accordance with the TDDframe configuration. The user device allocates a transmissions resourceto a D2D discovery signal within the discovery time interval accordingto the D2D discovery configuration. The D2D discovery signal istransmitted by the user device during the discovery time interval. Theuser device also receives from another user device a second D2Ddiscovery signal during the discovery time interval according to the TDDconfiguration and the D2D discovery configuration.

In accordance with another embodiment, a network component for TDDcommunications includes at least one processor and a computer readablestorage medium storing programming for execution by the at least oneprocessor. The programming includes instructions to select a TDD frameconfiguration from a set of available TDD frame configurations, and sendan indicator of the TDD frame configuration to a plurality of devices.The instructions further configure the network component to determine aD2D discovery configuration for a discovery time interval according tothe TDD frame configuration, and send, to the plurality of devices, theD2D discovery configuration. The D2D discovery configuration includesparameters enabling the devices to determine transmission resources ofD2D discovery signals and transmit the D2D discovery signals during thediscovery time interval.

In accordance with yet another embodiment, a user device fordevice-to-device (D2D) and time division duplexing (TDD) communicationsincludes at least one processor and a computer readable storage mediumstoring programming for execution by the at least one processor. Theprogramming includes instructions to receive an indicator of a TDD frameconfiguration selected from a set of available TDD frame configurations,and receive a D2D discovery configuration for a discovery time intervalin accordance with the TDD frame configuration. The user device isfurther configured to allocate a transmissions resource to a D2Ddiscovery signal within the discovery time interval according to the D2Ddiscovery configuration, and transmit the D2D discovery signal duringthe discovery time interval. The programming includes furtherinstructions to receive, from another user device, a second D2Ddiscovery signal during the discovery time interval according to the TDDconfiguration and the D2D discovery configuration.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates an example of a discovery/cellular subframepartition;

FIG. 2 illustrates a base station or network operation according to anembodiment of the disclosure;

FIG. 3 illustrates a user equipment (UE) operation according to anembodiment of the disclosure;

FIG. 4 illustrates a base station or UE operation according to anembodiment of the disclosure;

FIG. 5 illustrates a base station operation according to an embodimentof the disclosure;

FIG. 6 illustrates a base station operation according to an embodimentof the disclosure;

FIG. 7 illustrates a UE operation according to an embodiment of thedisclosure; and

FIG. 8 is a diagram of a processing system that can be used to implementvarious embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

One D2D technique is discovery. The discovery technique includes theability for a user equipment (UE) to discover neighboring UEs anddevices. A general description of discovery is that of one or more UEstransmitting D2D discovery signal(s) while one or more UEs attempt toreceive those D2D discovery signal(s). The number of UEs transmitting,the number of UEs receiving, and the number/type of signals may vary inaccordance with configuration/operation. For instance, discovery can beeither network/base station-assisted or open discovery. Withnetwork/base station-assisted discovery, one UE is directed to transmita signal (e.g., a Sounding Reference Signal (SRS) signal), and anotherUE is required to listen and report the signal quality to the basestation, for example a communications controller/network device such asan evolved node B (eNB). The eNB can, based on this reported signalquality, decide if Proximity-based Services (ProSe) can be enabled forthese two UEs. With open discovery, any UE can transmit a “beacon”signal to advertise its presence to other UEs. This process can possiblyinvolve idle UEs (e.g., UEs in the idle state). Given that opendiscovery involves idle UEs, it is performed with limited availableinformation. These UEs typically have to rely on the informationbroadcasted by the eNB, such as the system information block (SIB) ormaster information block (MIB). It would be relatively costly (in termsof power and network signaling) for most of the cases to wake up theseUEs and transmit Radio Resource Control (RRC) or other higher layersignaling to them. Furthermore, the location of idle UEs is approximate,and the exact cell where they camp may not be known by the network.

Discovery transmissions may occur on the uplink (UL) portion of thebandwidth since the interference would be less prejudicial to cellularUEs on the UL than on the downlink (DL). In general, the bandwidth forthe uplink can be different than the bandwidth for the downlink. Intypical deployments, the bandwidths for the uplink and downlink areequal. On the UL, a transmission of a D2D discovery signal may interferewith the reception of cellular signals at the eNB. Consequently, as longas the D2D UE is at a reasonable distance from the eNB and/ortransmitting with power restrictions, the interference created by theD2D discovery signal transmission has little impact. A D2D UE is a UEcapable of transmitting D2D discovery signals as well as receiving D2Ddiscovery signals. The D2D UE supports transmitting and receivingcellular signals. Conversely, on the DL, interference from D2D discoverysignal transmissions can affect neighboring UEs and potentiallydisrupt/hinder their ability to receive synchronization channels andphysical downlink control channels (PDCCHs), which can result insignificantly higher impact than if the D2D UE is transmitting D2Ddiscovery signals on the UL.

Embodiments are provided herein to ensure that D2D discovery signals aretransmitted on an uplink subframe when there is a TDD frameconfiguration change, e.g., when a TDD frame configuration orreconfiguration is transmitted. A plurality of schemes herein considerthat TDD frame configurations can change at higher frequency thanchanges to D2D discovery configuration. The embodiment schemes work forin-coverage UEs. Some of the embodiments also work for in-extendedcoverage UEs, e.g., when UEs are able to receive primary synchronizationsignals (PSS)/secondary synchronization signals (SSS), possibly afterseveral transmissions.

Many cellular systems employ time division multiple access and useframes and subframes to mark transmissions opportunities. In one system,long term evolution (LTE), each subframe is 1 millisecond in durationand there are 10 subframes in each frame. The subframes are numbered 0through 9. FIG. 1 shows an example of a discovery/cellular subframepartition 100 in a cellular or wireless network. The partition 100reflects the frequency of discovery subframes versus cellular subframes.For open discovery, a given number of available subframes (e.g., about1% of the subframes) can be reserved for discovery, while the remainingsubframes are used as for cellular communications. During the discoverysubframes, there usually are no cellular communications in the network.Only UE D2D discovery signals may be transmitted during the discoverysubframes 120. Some D2D UEs may transmit D2D discovery signals whileother D2D UEs may attempt to receive D2D discovery signals during thediscovery subframe.

For TDD systems, there are several possible configurations for a radioframe in terms of UL/DL subframes as well as special subframes. Forexample, Table 1 below shows a set of possible TDD frame configurationsfor 3GPP Rel-11, which are also indicated in Table 4.2-2 of the 3GPPTechnical Specification (TS) 36.211. In Table 1, “D” represents a DLsubframe, “U” represents an UL subframe, and “S” represents a specialsubframe, which may comprise UL and DL portions (symbols).

TABLE 1 TDD uplink-downlink configurations. Uplink- Downlink- Downlinkto-Uplink Config- Switch-point Subframe number uration periodicity 0 1 23 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U D DD D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D

TDD frame reconfiguration can occur relatively often in a cellular orwireless network. For instance, in Rel-11 and earlier releases, the TDDreconfiguration is done by sending a new System Information Block 1(SIB1) message. For Rel-12, in the context of the International MobileTelecommunication Advanced (IMTA) work item, other faster TDDconfiguration mechanisms are discussed, e.g., as summarized in 3GPP RANIcontribution R1-130883. The discussed options include RRC signaling,Physical broadcast channel (PBCH), Media Access Control (MAC) signaling,and Physical (PHY) layer signaling. Such reconfiguration options wouldnot be received by idle UEs. Since the set of TDD frame configurationsare known to both the eNB and the UEs, the eNB can transmit an indicatorof a selected TDD frame configuration, such as an index between 0 and 6.

It is likely that the D2D discovery reconfiguration would notchange/occur very frequently in the network. On the other hand, the TDDconfiguration can change relatively frequently, especially with thestandardization of IMTA. The idle UEs may not be notified of these TDDconfiguration changes. Since it is preferable to have the D2D subframeson the UL, as described above, it is practical and desirable to have amechanism which ensures that the D2D discovery subframes remain on theUL when TDD reconfiguration occurs. Additionally, the mechanism may needto work properly for inter-cell D2D discovery, e.g., in the case of asynchronized network.

A plurality of embodiment schemes are provided herein to ensure that theD2D discovery subframes are transmitted on the UL. In an embodimentscheme, the transmission of a D2D discovery is restricted to subframe 2for TDD UL/DL configurations, as shown in Table 1 (or Table 4.2-2 of3GPP TS 36.211). When looking at Table 1, it can be seen that subframe 2is always UL, regardless of the TDD frame configuration. The network orbase station, e.g., an eNB, can use a rule that the discovery subframeis always transmitted on subframe 2. As such, the UE does not need toknow the TDD frame configuration. One implication is that the discoverysubframe interval is a multiple of 10 millisecond (ms). This schemeprovides a compact way to signal which subframes are discoverysubframes, which can reduce the frequency of transmitting D2D discoveryconfiguration for idle UEs that need to get this message while poweringon. In another rule, a compact way to signal where the discoverysubframes are located is to send the following: an initial radio frameindex r, and a spacing index i. The receiving UE interprets this messageas follows: the first discovery subframe is subframe 2 in radio frame r,the next is subframe 2 in radio frame r+i, then subframe 2 in radioframe r+2i, and so forth. The addition is modulo. For instance, in LTE,the frames are numbered 0 to 1023. If the value of (r+ki) exceeds 1023for some integer k, the frame is (r+ki) modulo 1024. This approach mayimpose certain restrictions on both discovery and cellular operations,considering UL subframes may be used for other applications.

Other embodiment schemes include alternatives to place the discoverysubframes at desired transmission locations. For instance, the networkmay locate the discovery subframe on other subframes than subframe 2.This can be achieved by noticing that in Table 1, except for TDD frameconfigurations 2 and 5, all the other configurations have subframe 3 asUL. Thus, another way to achieve the goal of having discovery subframeson the UL is to prohibit the use of TDD frame configurations 2 and 5 ina radio frame where D2D discovery transmission occurs and to always usesubframe 3 for transmitting the D2D discovery signal during thediscovery subframe. In another example, another alternative embodimentcomprises using subframe 7 as discovery subframe and preventing the useof TDD frame configurations 3, 4, and 5.

The embodiment further comprises a scheme in which RRC-connected modeUEs can be assigned a second set of discovery subframe locations. Theset can be signaled to idle UEs as well. The network can instruct UEs toalways listen for D2D discovery signals in the second set. In analternative approach, each UE uses a pseudo-random binary sequencegenerator to decide whether it is going to listen to discovery messagespotentially transmitted in the second set. The probability ruleassociated to the pseudo-random binary generator can be signaled by thenetwork. Assigning such a set may help in faster discovery of theinformation conveyed in the D2D discovery signals transmitted byRRC-connected UEs. The RRC-connected UEs may be aware of the actual TDDframe configuration and therefore, they can transmit for instance insubframe 3 if they have been instructed to do so and if subframe 3 is anUL subframe in the present TDD frame configuration. The RRC-connectedUEs that are not transmitting D2D discovery signals may listen to D2Ddiscovery signals transmitted by other RRC-connected UEs in suchsubframes.

In yet other embodiments, a similar scheme can be used on the DL insteadof UL. For instance, by noting that subframe 5 is always DL, subframe 5can be used for D2D discovery no matter the TDD frame configuration.Assuming that the UEs decode SIB1, and that the TDD frame configurationis always indicated by SIB1, other rules can also be implemented. Forinstance, the D2D discovery subframe can have priority over the DLcellular subframe. Another rule can be the discovery subframe isrestricted to odd numbered frames (1, 3, . . . ) since SIB1 istransmitted from the eNB on subframe 5 every even numbered frame.

In another embodiment, the uplink pilot timeslot (UpPTS) portion of aspecial subframe can be used for D2D discovery. When looking at Table 1,subframe 1 is a special subframe among the configurations. A specialsubframe contains a downlink portion, e.g., a downlink pilot timeslot(DwPTS), some guard time, and an uplink pilot timeslot (UpPTS). There isa listing of special subframe configurations with various combinationsof symbols for the DwPTS and UpPTS in Table 4.2-1 of 3GPP TS 36.211. TheUpPTS portion of the subframe is short, and in practice, may not beuseful for certain cellular transmissions, such as the Physical UplinkShared Channel (PUSCH) transmission. In various deployments, the UpPTSsection is unused for uplink signal transmission since it is only 1 to 2symbols in length. Thus, the D2D discovery signal may be transmitted inthe UpPTS section of the special subframe. Deploying this solution issimilar to deploying the solution described above using the subframe 2for D2D discovery. However, the solution using the UpPTS portion of thespecial subframe for D2D discovery may place some constraints on the D2Ddiscovery signal design. For example, the D2D discovery signal may haveto be transmitted on at most 1 symbol, since the minimum UpPTS length is1 symbol. The random access channel (RACH) can be supported on thespecial subframe even when there is one uplink symbol for certainspecial subframe configurations. Because the RACH requires two symbols,the standard allows some guard time to be used for RACH transmission.The usage of guard time for certain special subframe configurations canbe extended for the discovery, and thus allows the D2D discovery signalto be transmitted over two symbols. The duration of one symbol isapproximately 1/14^(th) of a subframe for certain cyclic prefixconfigurations.

Another embodiment based on the special subframe is to reserve severalsymbols of DwPTS for discovery. As noted, subframe 1 is always a specialsubframe. Due to overhead transmitted by the eNB in the first 3 symbolsof the DwPTS, the first 3 symbols of DwPTS may be inappropriate fordiscovery. Although several special subframe configurations have theDwPTS as 3 symbols, other configurations have longer durations, such as6 symbols. The symbols that are not reserved for cellular transmissionsin the DwPTS can be used for discovery. For example, special subframeconfiguration 1 (Table 4.2-1 of 36.211) has a DwPTS of 9 symbols. A partof the DwPTS, for instance the last 6 symbols (the symbols following thefirst 3 symbols of the DwPTS), can be reserved for discovery. Someportion of the DwPTS symbols reserved for discovery may be used forswitching between transmit and receive modes. In another embodiment,subframe 6 is either a special subframe or a DL subframe. A similarusage of symbols after the first 3 symbols of the subframe can be usedfor discovery.

In another embodiment, a combination of the aforementioned discoverylocations can be used. In particular, discovery resources may beavailable in UpPTS (1-2 symbols) and/or in DwPTS (for some specialsubframe configurations), and/or in other subframes (like subframe #2).

The embodiment further comprises having different discovery resourcesizes corresponding to the location of D2D discovery signal. In anexample, a discovery resource is 1RB in subframe 2 and 6 RBs in UpPTS(having a 2-symbol length). These resources can be located in same ordifferent radio frames.

In another embodiment, the discovery subframes are allowed to be eitherUL or DL. One possible implementation is based on that for TDD, whetherthe subframe is DL or UL, the interference level in the cellular systemis the same as long as only D2D discovery signals are transmitted.Consequently, it is possible to allow discovery to be performed eitheron an UL or DL subframe, as long as no cellular transmission occurs.Hence, at least in theory, doing nothing other than allowing discoverysubframes to be either DL and UL is enough. While this solution maywork, it may be in practice difficult to implement. Since there are moresignals and channels transmitted on specific subframes of the DL (e.g.,PBCH, SIBs), having DL D2D discovery subframes may result in thesesubframes colliding with the subframes where these DL channels aretransmitted. This could cause some backwards probability problems.Furthermore, the UE needs to perform channel measurements on the DL. Ifthe UE happens to perform channel measurements on a discovery subframe,the measurements may be incorrect. Consequently, while possible, thissolution may not be a preferred solution to have DL discovery subframes.

In another embodiment, a subframe configured as a Multicast-BroadcastSingle Frequency Network (MBSFN) subframe is used for signaling the D2Ddiscovery on the DL. For instance, subframes 0 or 5 in Table 1 can beused, since these subframes are always DL subframes. One solution is toperiodically configure a DL subframe as a MBSFN subframe. All the UEsneed to know when this subframe occurs (e.g., by specification, byhaving its location broadcasted, and by any other suitable means). Theperiodically scheduled MBSFN subframe is reserved for D2D discovery.Since this is an MBSFN subframe, it can be empty, except for thecell-specific reference signal (CRS) in symbol 0, and possibly 1 if 4CRS ports are used, of the subframe, if the eNB does not send any grantsin the PDCCH region (e.g., first few symbols of the subframe) for thissubframe and if no Semi-Persistent Scheduling (SPS) transmission isscheduled. The D2D UEs can transmit their D2D discovery signals in oneof these scheduled subframes. With some guard time, it is possible tohave the D2D discovery signal sent in the empty or blank part of theMBSFN subframe. It may also be possible to send the D2D discovery signalat the same time as the CRS on symbol 0 of the MBSFN subframe, althoughthis would create some interference, e.g., for the receiving UEs closeto the eNB. The CRS interference impact may be more in case of having acluster of small cells. However, the cellular UEs are not affected bythis increase in interference. The scheme may also suffer fromadditional discovery performance degradation in the presence of atransmission power hopping mechanism allowing a UE to transmit its D2Ddiscovery signal with a smaller power than its maximum transmit power.

In another embodiment, a new D2D discovery configuration is broadcastedevery time a new TDD frame configuration is selected. The new D2Ddiscovery configuration broadcast message can occur on the PBCH, whichconveys the MIB, or a SIB message. While relatively easy, this solutionmay have drawbacks. The TDD frame configuration may change quite often,since it adapts to the instantaneous traffic demand. On the other hand,the D2D discovery configuration may not need to change that often sinceit adapts to the density of present users, which may more stable thanthe traffic demand. In idle mode, a UE may not listen very often to thecontrol channels (e.g., PBCH, PDCCH). In order not to miss any message,an idle UE would have to listen more often, resulting in increased powerconsumption. In addition, the D2D discovery configuration needs to besent out quite often, resulting in high overhead for the system.

In another embodiment, a new D2D discovery configuration is broadcastedevery time the TDD frame configuration is broadcasted, as in thesolution above. An additional step is implemented. The UE knows where ULsubframes are located. However, according to the broadcasted D2Ddiscovery configuration, the D2D discovery subframe may coincide withthe UL subframes. Therefore, an additional rule is that when the D2Ddiscovery subframe does not coincide with the UL subframe, the UEselects the closest UL subframe for the D2D discovery subframe. Theclosest UL subframe may be the first UL subframe after where the D2Dsubframe should be, or before, or any similar criterion. The closest ULsubframe can mean: the first UL subframe after where the discoverysubframe should be, or before, or any similar criterion.

FIG. 2 illustrates a base station or network operation 130 forconfiguring D2D discovery at a plurality of UEs. At step 201, the basestation or network component selects a TDD frame configuration from aset of available TDD frame configurations. The base station furtherdetermines a suitable D2D discovery configuration according to the TDDframe configuration, for instance to ensure that D2D discovery signalsare transmitted on an uplink subframe when there is a TDD frameconfiguration change. At step 202, the base station or network componentsends an indicator of the TDD frame configuration and the D2D discoveryconfiguration to a plurality of UEs. The D2D discovery configurationincludes parameters that enable the UEs to determine transmissionresources of D2D discovery signals and transmit the D2D discoverysignals during the discovery time interval.

FIG. 3 illustrates a UE operation 140 for handling transmissions of D2Ddiscovery signals. At step 301, the UE receives, from a base station orthe network, an indicator of a TDD frame configuration selected from aset of available TDD frame configurations, and a D2D discoveryconfiguration for a discovery time interval in accordance with the TDDframe configuration. At step 302, the UE allocates a transmissionsresource to a D2D discovery signal within the discovery time intervalaccording to the D2D discovery configuration. At step 303, the UEtransmits the D2D discovery signal during the discovery time interval.At step 304, the UE receives, from another user device, a second D2Ddiscovery signal during the discovery time interval according to the TDDconfiguration and the D2D discovery configuration.

FIG. 4 shows a base station or UE operation method 200 for determiningwhether a subframe is a D2D discovery subframe. Note that having apredefined subframe can also apply to a FDD system (systems that supportFDD and TDD), and would lead to a similar logic, with minor changes. Themethod 200 may be used in any suitable embodiment of the embodimentsdescribed above. In the case of a base station, e.g., an eNB,implementing the method 200, the eNB determines, in step 210, thecurrent subframe number N (N is an integer). For example N can rangefrom 0 to 9 for LTE Rel-11.

In step 220, the eNB determines if subframe N should be a subframe forD2D discovery signal transmission among UEs according to the D2Ddiscovery configuration or the scheme adopted. One example is comparingthe current frame number to the frame number when a discovery subframeis to be sent. If the result of the decision step 220 is yes, then theeNB determines, in step 230, if the current subframe N is an uplinksubframe. Otherwise, the method 200 ends. If the result of the decisionstep 230 is yes, then, in step 240, the eNB assigns subframe N as a D2Ddiscovery subframe. Otherwise, in step 250, the eNB configures the nextuplink subframe following subframe N as a D2D discovery subframe. Notethat this last step is optional, and may not be necessary for someembodiments.

In the case of a UE implementing the method 200, the UE, in step 210,determines the current subframe number N. In step 220, the UE determinesif subframe N should be a subframe where the D2D discovery signal shouldbe sent according to the D2D discovery configuration or the schemeadopted. If not, then the method 200 ends. If yes, then the UEdetermines, in step 230, if the current subframe N is an uplinksubframe. If yes, then in step 240, the UE processes subframe N as a D2Ddiscovery subframe. If not, then in step 250, the UE treats the nextuplink subframe following subframe N as a discovery subframe. Note thatthis last step is optional, and may not be necessary for someembodiments.

FIG. 5 shows a base station operation method 300 that may be used in anysuitable embodiment of the embodiments described above, for instance inthe case of using the MBSFN subframe for D2D discovery. The method 300implies that the base station, e.g., an eNB, has previously sent a D2Ddiscovery configuration and a MBSFN configuration with no error, e.g.,indicating that the D2D discovery subframe is always on a MBSFNsubframe. If that is not the case, an operation similar to that inmethod 200 can also be implemented to determine where to locate the D2Ddiscovery subframe. In step 310 of the method 300, the eNB determinesthe current DL subframe N. In step 320, the eNB determines if subframe Nshould be a subframe where the D2D discovery signal is sent according tothe D2D discovery configuration or the scheme adopted. If not, then themethod 300 ends. If yes, then in step 330, the eNB does not schedule anytransmission during the subframe. In step 340, the eNB configuressubframe N as D2D subframe.

FIG. 6 shows a base station operation method 400 that may be used in anysuitable embodiment of the embodiments described above, for instance inthe case of broadcasting (e.g., on a PBCH or SIB message) a new D2Ddiscovery configuration every time a new TDD configuration is selected.In step 410, the base station, e.g., communications controller or eNB,decides to use a new D2D discovery configuration. In step 420, the eNBencodes a new SIB message accordingly. In step 430, the eNB transmitsthe new SIB as well as the resource allocation for transmitting thisSIB.

FIG. 7 shows a UE operation method 500 that may be used corresponding tothe operation method 400 of the base station, for instance in the caseof broadcasting (e.g., on a PBCH or SIB message) a new D2D discoveryconfiguration every time a new TDD configuration is selected. In step510, the UE monitors the common PDCCH search space on some subframes todetermine if the SIB containing the new discovery allocation istransmitted. If it is determined in step 520 that a SIB is transmitted,the UE decodes the SIB in step 530, and the method 500 proceeds to step540. Otherwise, the method 500 ends. If it is determined in step 540that the SIB includes a new D2D discovery configuration, the UE switchesto the new discovery configuration in step 550. Otherwise, the UEcontinues to use the previous discovery configuration in step 560.

FIG. 8 is a block diagram of an exemplary processing system 600 that canbe used to implement various embodiments. Specific devices may utilizeall of the components shown, or only a subset of the components andlevels of integration may vary from device to device. Furthermore, adevice may contain multiple instances of a component, such as multipleprocessing units, processors, memories, transmitters, receivers, etc.The processing system 600 may comprise a processing unit 601 equippedwith one or more input/output devices, such as a network interfaces,storage interfaces, and the like. The processing unit 601 may include acentral processing unit (CPU) 610, a memory 620, a mass storage device630, and an I/O interface 660 connected to a bus. The bus may be one ormore of any type of several bus architectures including a memory bus ormemory controller, a peripheral bus or the like.

The CPU 610 may comprise any type of electronic data processor. Thememory 620 may comprise any type of system memory such as static randomaccess memory (SRAM), dynamic random access memory (DRAM), synchronousDRAM (SDRAM), read-only memory (ROM), a combination thereof, or thelike. In an embodiment, the memory 620 may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms. In embodiments, the memory 620 is non-transitory. The massstorage device 630 may comprise any type of storage device configured tostore data, programs, and other information and to make the data,programs, and other information accessible via the bus. The mass storagedevice 630 may comprise, for example, one or more of a solid statedrive, hard disk drive, a magnetic disk drive, an optical disk drive, orthe like.

The processing unit 601 also includes one or more network interfaces650, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or one or more networks 680.The network interface 650 allows the processing unit 601 to communicatewith remote units via the networks 680. For example, the networkinterface 650 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing unit 601 is coupled to alocal-area network or a wide-area network for data processing andcommunications with remote devices, such as other processing units, theInternet, remote storage facilities, or the like.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method for device-to-device (D2D) discovery intime division duplexing (TDD) communications, the method comprising:selecting, at a network component, a TDD frame configuration from a setof available TDD frame configurations; sending, from the networkcomponent, an indicator of the TDD frame configuration to a plurality ofdevices; determining a D2D discovery configuration for a discovery timeinterval according to the TDD frame configuration; and sending, from thenetwork component to the plurality of devices, the D2D discoveryconfiguration, wherein the D2D discovery configuration includesparameters relating to resources of D2D discovery signals andtransmission of the D2D discovery signals during the discovery timeinterval.
 2. The method of claim 1, wherein the discovery time intervalcorresponds to defined symbols in a designated subframe or multiplesubframes of the set of available TDD frame configurations.
 3. Themethod of claim 2, and wherein the set of available TDD configurationsincludes configurations 0 to 6, wherein configuration 0 comprisescorresponding subframes 0 and 5 on downlink bandwidth, subframes 1 and 6defined as special subframes including an uplink bandwidth portion and adownlink bandwidth portion, and subframes 2, 3, 4, 7, 8, and 9 on uplinkbandwidth, wherein configuration 1 comprises corresponding subframes 0,4, 5, and 9 on downlink bandwidth, subframes 1 and 6 defined as specialsubframes, and subframes 2, 3, 7, and 8 on uplink bandwidth, whereinconfiguration 2 comprises corresponding subframes 0, 3, 4, 5, 8 and 9 ondownlink bandwidth, subframes 1 and 6 defined as special subframes, andsubframes 2, and 7 on uplink bandwidth, wherein configuration 3comprises corresponding subframes 0, 5, 6, 7, 8 and 9 on downlinkbandwidth, subframe 1 defined as a special subframe, and subframes 2, 3,and 4 on uplink bandwidth, wherein configuration 4 comprisescorresponding subframes 0, 4, 5, 6, 7, 8 and 9 on downlink bandwidth,subframe 1 defined as a special subframe, and subframes 2, and 3 onuplink bandwidth, wherein configuration 5 comprises correspondingsubframes 0, 3, 4, 5, 6, 7, 8 and 9 on downlink bandwidth, subframe 1defined as a special subframe, and subframe 2 on uplink bandwidth, andwherein configuration 6 comprises corresponding subframes 0, 5, and 9 ondownlink bandwidth, subframes 1 and 6 defined as special subframes, andsubframes 2, 3, 4, 7 and 8 on uplink bandwidth.
 4. The method of claim3, wherein, according to the D2D discovery configuration, thetransmissions of the D2D discovery signals are on the uplink bandwidth.5. The method of claim 3, wherein, according to the D2D discoveryconfiguration, the transmissions of the D2D discovery signals are on thedownlink bandwidth.
 6. The method of claim 5, wherein the designatedsubframe is a common subframe on the downlink bandwidth for allconfigurations in the set of available TDD configurations.
 7. The methodof claim 5, wherein the designated subframe is subframe 5 in the set ofavailable TDD configurations.
 8. The method of claim 5, wherein thedesignated subframe is a Multicast-Broadcast Single Frequency Network(MBSFN) subframe.
 9. The method of claim 3, wherein the designatedsubframe is a special subframe in the set of available TDDconfigurations, and comprising both an uplink bandwidth portion and adownlink bandwidth portion of symbols.
 10. The method of claim 9,wherein the designated subframe is subframe 1 in the set of availableTDD configurations.
 11. A method for device-to-device (D2D) discovery intime division duplexing (TDD) communications, the method comprising:receiving, at a user device, an indicator of a TDD frame configurationselected from a set of available TDD frame configurations; receiving, atthe user device, a D2D discovery configuration for a discovery timeinterval in accordance with the TDD frame configuration; allocating atransmissions resource to a D2D discovery signal within the discoverytime interval according to the D2D discovery configuration;transmitting, from the user device, the D2D discovery signal during thediscovery time interval; and receiving, at the user device from anotheruser device, a second D2D discovery signal during the discovery timeinterval according to the TDD configuration and the D2D discoveryconfiguration.
 12. The method of claim 11 wherein, the indicator of theTDD frame configuration is received via higher layer signaling.
 13. Themethod of claim 11, wherein the discovery time interval corresponds toallocated symbols in a designated subframe of multiple subframes of theset of available TDD frame configurations, and wherein the D2D discoverysignal is transmitted only using the allocated symbols on the designatedsubframe.
 14. The method of claim 13, and wherein the set of availableTDD configurations includes configurations 0 to 6, wherein configuration0 comprises corresponding subframes 0 and 5 on downlink bandwidth,subframes 1 and 6 defined as special subframes including an uplinkbandwidth portion and a downlink bandwidth portion, and subframes 2, 3,4, 7, 8, and 9 on uplink bandwidth, wherein configuration 1 comprisescorresponding subframes 0, 4, 5, and 9 on downlink bandwidth, subframes1 and 6 defined as special subframes, and subframes 2, 3, 7, and 8 onuplink bandwidth, wherein configuration 2 comprises correspondingsubframes 0, 3, 4, 5, 8 and 9 on downlink bandwidth, subframes 1 and 6defined as special subframes, and subframes 2, and 7 on uplinkbandwidth, wherein configuration 3 comprises corresponding subframes 0,5, 6, 7, 8 and 9 on downlink bandwidth, subframe 1 defined as a specialsubframe, and subframes 2, 3, and 4 on uplink bandwidth, whereinconfiguration 4 comprises corresponding subframes 0, 4, 5, 6, 7, 8 and 9on downlink bandwidth, subframe 1 defined as a special subframe, andsubframes 2, and 3 on uplink bandwidth, wherein configuration 5comprises corresponding subframes 0, 3, 4, 5, 6, 7, 8 and 9 on downlinkbandwidth, subframe 1 defined as a special subframe, and subframe 2 onuplink bandwidth, and wherein configuration 6 comprises correspondingsubframes 0, 5, and 9 on downlink bandwidth, subframes 1 and 6 definedas special subframes, and subframes 2, 3, 4, 7 and 8 on uplinkbandwidth.
 15. The method for claim 14, wherein, in accordance with theD2D discovery configuration, the D2D discovery signal is transmittedonly on the uplink bandwidth.
 16. The method of claim 15, wherein thedesignated subframe is subframe 2 in the set of available TDDconfigurations.
 17. The method of claim 15, wherein the designatedsubframe is subframe 3 in configurations 0, 1, 3, 4, and 6 in the set ofavailable TDD configurations.
 18. The method of claim 15, wherein thedesignated subframe is subframe 7 in configurations 0, 1, 2, and 6 inthe set of available TDD configurations.
 19. The method for claim 14,wherein, in accordance with the D2D discovery configuration, the D2Ddiscovery signal is transmitted only on downlink bandwidth.
 20. Themethod of claim 19, wherein the designated subframe is subframe 0 or 5in the set of available TDD configurations.
 21. The method of claim 19,wherein the designated subframe is a Multicast-Broadcast SingleFrequency Network (MBSFN) subframe.
 22. The method of claim 14, whereinthe designated subframe is a special subframe.
 23. The method of claim22, wherein the special subframe comprises both an uplink portion and adownlink portion of symbols, and wherein the method further comprisesdetecting the D2D discovery signal on the uplink bandwidth portion ofthe special subframe in accordance with the D2D discovery configuration.24. A network component for time division duplexing (TDD)communications, the network component comprising: at least oneprocessor; and a computer readable storage medium storing programmingfor execution by the at least one processor, the programming includinginstructions to: select a TDD frame configuration from a set ofavailable TDD frame configurations; send an indicator of the TDD frameconfiguration to a plurality of devices; and determine a D2D discoveryconfiguration for a discovery time interval according to the TDD frameconfiguration; and send, to the plurality of devices, the D2D discoveryconfiguration, wherein the D2D discovery configuration includesparameters relating to resources of D2D discovery signals andtransmission of the D2D discovery signals during the discovery timeinterval.
 25. The network component of claim 24, wherein the discoverytime interval corresponds to defined symbols in a designated subframe ormultiple subframes of the set of available TDD frame configurations. 26.The network component of claim 25, wherein, according to the D2Ddiscovery configuration, the transmissions of the D2D discovery signalsare on uplink bandwidth.
 27. The network component of claim 25, wherein,according to the D2D discovery configuration, the transmissions of theD2D discovery signals are on downlink bandwidth.
 28. The networkcomponent of claim 27, wherein the designated subframe is aMulticast-Broadcast Single Frequency Network (MBSFN) subframe.
 29. Thenetwork component of claim 25, wherein the designated subframe is aspecial subframe comprising an uplink bandwidth portion and a downlinkbandwidth portion, and wherein, according to the D2D discoveryconfiguration, the transmissions of the D2D discovery signals are onlyon the uplink bandwidth portion or only on the downlink bandwidthportion.
 30. The network component of claim 24, wherein the networkcomponent is a base station.
 31. A user device configured fordevice-to-device (D2D) and time division duplexing (TDD) communications,the user device comprising: at least one processor; and a computerreadable storage medium storing programming for execution by the atleast one processor, the programming including instructions to: receivean indicator of a TDD frame configuration selected from a set ofavailable TDD frame configurations; receive a D2D discoveryconfiguration for a discovery time interval in accordance with the TDDframe configuration; allocate a transmissions resource to a D2Ddiscovery signal within the discovery time interval according to the D2Ddiscovery configuration; transmit the D2D discovery signal during thediscovery time interval; and receive, from another user device, a secondD2D discovery signal during the discovery time interval according to theTDD configuration and the D2D discovery configuration.
 32. The userdevice of claim 31, wherein the discovery time interval corresponds toallocated symbols in a designated subframe of multiple subframes of theset of available TDD frame configurations, and wherein the instructionsto transmit the D2D discovery signal include instructions to transmitthe D2D discovery signal only using the allocated symbols on thedesignated subframe.